Presently many LANs have users that communicate with each other over a common communication channel. Each user is physically connected to the communication channel by ports, and transmits and receives information back and forth from the communication channel through the ports.
Many LAN connection systems provide a flexible means of configuring the number of ports. This is often accomplished by partitioning groups of ports onto individual modules, which then may be installed into a communications concentrator. A common information bus built within the backplane of the concentrator allows individual modules to be interconnected to act as a single communications system.
In the "ETHERNET".TM. LAN each user is given a unique address and information is transmitted in data packets over a communication channel known as a backplane bus. Each data packet has a source address indicating which user generated the data packet and each data packet also has a destination address indicating for which user the data packet is intended. Each user listens to the communication channel and when it hears its own address as the destination address of a data packet, the user knows that the data packet is intended for itself.
Disadvantages of this system are that any user connected to a port can hear and receive all the data packets that are transmitted onto the backplane bus. Also any user can physically connect to a port and transmit information or instructions over the backplane bus.
U.S. Pat. No. 4,899,333 to Roediger discloses a system with a switching distribution network. Data packets are received by the data switching modules, and these data switching modules read the destination address of the modules and decide on which one a plurality of paths to send the data packet. The data switching modules provide a small measure of security, in that data packets are not sent to paths where they do not belong. The main disadvantage of such switching systems is the cost and complexity of the switching modules.
An attempt has been made to provide a more secure LAN in U.S. Pat. No. 5,161,192 to Carter et al. This patent discloses a system in which several ports are connected to a repeater. Each repeater has its own rules for which signals can be received and then retransmitted to its ports. If a signal fails these rules for any reason, a portion of the signal is modified to make it unreadable. All the ports of one repeater either all receive the same signal or receive the modified signal. There is no differentiating between ports of the same repeater. All ports of one repeater must obey the same set of rules.
Clearly then several repeaters must be connected together in order to be able to differentiate between groups of ports. Carter therefore requires a separate repeater for each set of rules and the sub group that follows those rules. Carter then usually requires another repeater to connect the individual repeaters. Many networks do not need or can afford this many repeaters. The number of repeaters gets excessively high when each port is required to be secure and only receive data packets for itself. In Carter each port would then need its own repeater with its own set of rules.
U.S. Pat. No. 5,177,788 to Schanning et al, describes a system where several repeaters are connected to a backbone. Each of these repeaters checks the addresses of the data packets transmitted into the repeater by any of the ports of the repeater. If any of these addresses indicate that a port is not to receive the data packet, an individual and separate signal is sent to each of the ports over a discrete line. A jam pattern is also sent from the repeater to each individual port. Depending on the separate individual signal that each port receives over its own discrete line, the port decides whether or not to pass the data packet or the jam pattern to the user of the port. The disadvantage of this system is that it is limited to repeaters and each repeater must individually check each data packet coming into the computer. Also there must be a separate and individual line from the repeater to each port, directly telling each port whether or not to pass the data packet or the jam pattern. As the number of ports increases, it quickly becomes impractical to send each port an individual and separate signal.